The Nationals were leading, 3-1, in the third inning when the 19-year-old Harper hit a 2-1 pitch from right-hander Tim Stauffer over the center-field wall to give Washington a three-run lead.
"I was trying to go up there and get a knock. That's all I was worried about. I was trying to get something I could drive and go out of the ballpark," Harper said. "I have guys around me that are hitting very well. It gets a little easier when guys are hitting the ball."
Padres manager Bud Black came away impressed by what he saw from Harper on Monday.
"He's a talented, young player, an exciting, young player," Black said. "He plays hard, runs the bases hard and looks like a guy who takes an aggressive swing. At 19, that says something."
After touching home plate, Harper, playing in his 15th game, was given a curtain call. Harper wondered if he should acknowledge the crowd. But there was teammate Danny Espinosa, the next hitter, getting out of the batter's box, and the veterans, led by the injured Jayson Werth, telling Harper to go out there and acknowledge the fans. Harper did.
"I was pretty excited about that. I wasn't sure if I should have went up there, but all the veteran guys said to go get it, so I did. It was cool," Harper said.
Said manager Davey Johnson, "I thought the curtain call was great. I don't think it's going to calm [Harper] down any. I think that is impossible. But it's good to see him hit the ball hard."
Harper, who went 1-for-4 in the game, finished Monday's action hitting .232 with a homer and four RBIs.
"I was feeling a little antsy the past couple of series, but I feel good up there. When you have guys around you hitting, I think things get a little bit easier," he said.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.